Fix GH-20352: UAF in php_output_handler_free via re-entrant ob_start() during error deactivation #20356
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…rt() during error deactivation The problem is that the code is doing `php_output_handler_free` in a loop on the output stack, but prior to freeing the pointer on the stack in `php_output_handler_free` it calls `php_output_handler_dtor` which can run user code that reallocates the stack, resulting in a dangling pointer freed by php_output_handler_free. Furthermore, OG(active) is set when creating a new output handler, but the loop is supposed to clean up all handlers, so OG(active) must be reset as well.
Girgias
approved these changes
Nov 2, 2025
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The problem is that the code is doing
php_output_handler_freein a loop on the output stack, but prior to freeing the pointer on the stack inphp_output_handler_freeit callsphp_output_handler_dtorwhich can run user code that reallocates the stack, resulting in a dangling pointer freed by php_output_handler_free. Furthermore, OG(active) is set when creating a new output handler, but the loop is supposed to clean up all handlers, so OG(active) must be reset as well.